Method and apparatus for transmitting a power headroom report of a UE in a wireless communication system

ABSTRACT

A method and an apparatus are provided for transmitting a Power Headroom Report (PHR) to base station by a User Equipment (UE), wherein the UE determines whether a received an uplink resource is a first uplink resource allocated for a new transmission after a Medium Access Control (MAC) reset, and starts a timer for reporting the PHR, if the allocated uplink resource is the first uplink resource allocated for the new transmission after the MAC reset.

PRIORITY

This application is a Continuation of U.S. patent application Ser. No.12/725,916, which was filed in the U.S. Patent and Trademark Office onMar. 17, 2010, and claims priority under 35 U.S.C. § 119(a) to a KoreanPatent Application filed in the Korean Intellectual Property Office onMar. 17, 2009 and assigned Serial No. 10-2009-0022719, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method and apparatus fortransmitting scheduling information by a User Equipment (UE) in awireless communication system, and more particularly, to a method andapparatus for transmitting available transmit power information (or apower headroom report) by a UE in a wireless communication system.

2. Description of the Related Art

A Universal Mobile Telecommunication Service (UMTS) system is a 3^(rd)Generation (3G) wireless communication system that is based on GlobalSystem for Mobile communications (GSM) and General Packet Radio Services(GPRS), which are asynchronous communication systems, and uses WidebandCode Division Multiple Access (WCDMA). Previously, the 3^(rd) GenerationPartnership Project (3GPP) in charge of standardization of the UMTSsystem proposed a High Speed Downlink Packet Access (HSDPA)/High SpeedUplink Packet Access (HSUPA) system capable of supporting a data rate ofup to 10 Mbps in a downlink, as a wireless communication system providedby improving the UMTS system. Further, the HSDPA/HSUPA system has nowbeen commercialized and is now providing services.

Since the proposal of the HSDPA/HSUPA, the 3GPP has more recentlysuggested a Long Term Evolution (LTE) system as an evolvednext-generation wireless communication system. The LTE system willimplement high-speed packet-based communication at a data rate of up to100 Mbps. Accordingly, many studies are underway for commercializationthe LTE system.

In both the HSDPA/HSUPA system and LTE system proposed by the 3GPP, aNode B or Evolved Node B (ENB) receives scheduling information from UEsfor scheduling the allocation of transmission resources to the UEs. Thescheduling information may include, for example, UE buffer statusinformation, available transmit power information, etc.

The buffer status information is information with which the UE informsthe ENB of the amount of transmission data in a UE transmission buffer.The available transmit power information is information with which theUE informs the ENB of the amount of power available for uplinktransmission. Upon receiving the available transmit power information,the ENB performs scheduling in order to avoid a scheduling error by a UEmaximum output limit.

FIG. 1 illustrates a configuration of an LTE system.

Referring to FIG. 1, Evolved Radio Access Networks (E-RANs) 110 and 112are simplified to a 2-node configuration including ENBs 120, 122, 124,126, and 128, and upper nodes (also known as access gateways) 130 and132. A UE 101 accesses an Internet Protocol (IP) network 114 through theE-RANs 110 and 112. The ENBs 120 to 128 correspond to legacy Node Bs ofan existing UMTS system. Each of the ENBs 120 to 128 is connected to theUE 101 by a wireless channel, and performs complex functions whencompared with the function performed by legacy Node Bs.

In the LTE system, because every user traffic including a real-timeservice, like Voice over IP (VoIP), based on the Internet protocol, isserviced over a shared channel, an apparatus for performing schedulingby collecting status information of UEs is needed, and this schedulingis managed by the ENBs 120 to 128. Generally, one of the ENBs 120 to 128controls multiple cells. In FIG. 1, it is assumed that ENB 122 is thecontrolling ENB.

In order to implement a data rate of up to 100 Mbps, the LTE system usesOrthogonal Frequency Division Multiplexing (OFDM) as a wireless accesstechnology in a bandwidth of up to 20 MHz. In addition, the LTE systemuses Adaptive Modulation & Coding (AMC) to determine a modulation schemeand a channel coding rate according to UE channel status.

For example, ENB 122 receives reports on a variety of schedulinginformation from UE 101 in order to allocate transmission resources toUE 101, i.e., a scheduling operation. Examples of such schedulinginformation include the buffer status information or Buffer StatusReport (BSR) about an amount and type of data UE 101 stores in itstransmission buffer, and available transmit power information aboutavailable transmit power for UE 101.

The BSR is information indicating an amount of data UE 101 stores in itstransmission buffer for uplink transmission, according to the priority.If particular conditions are satisfied, UE 101 generates the BSR andtransmits it to ENB 122. For example, the particular conditions mayinclude a situation in which UE 101, which previously had no data storedin it, now has new data to transmit, and a situation in which apredetermined time has elapsed since a previous transmission of the BSR.

The available transmit power information is information indicating anavailable power that UE 101 can use for uplink data transmission, basedon its current channel status. The available transmit power informationis transmitted from UE 101 to the ENB 122 using a message of a MediumAccess Control (MAC) layer, and is commonly called an Uplink PowerHeadroom (UPH) or Power Headroom Report (PHR). In the followingdescription, the available transmit power information will be referredto as a PHR.

More specifically, the PHR is defined as a difference between a requiredtransmit power required for uplink transmission and a maximum transmitpower for UE 101, when UE 101 performs uplink transmission using thetransmission resource and Modulation & Coding Scheme (MCS) levelallocated from ENB 122. A method of calculating the PHR may be modifiedappropriately depending on system conditions.

If the following particular conditions are satisfied, UE 101 generatesthe PHR and then transmits it to the ENB 122.

Condition 1) A change in a path loss measured by UE 101 exceeds athreshold.

Condition 2) A predetermined time has elapsed since UE 101 transmittedthe PHR.

Before performing uplink transmission, UE 101 checks if any one of theabove two conditions is satisfied, and if so, includes a PHR in anuplink transmission packet during transmission. In the LTE system, apacket carrying the PHR includes a MAC Protocol Data Unit (PDU).

A PHR generated by Condition 1) is commonly referred to as a regularPHR, and a PHR generated by Condition 2) is commonly referred to as aperiodic PHR.

In the LTE system, generation of the periodic PHR is controlled by atimer, i.e., a PHR Periodic Timer. UE 101 starts the PHR Periodic Timerafter transmitting a periodic PHR, and when the PHR Periodic Timerexpires, UE 101 includes a next periodic PHR in a first MAC PDU beingtransmitted, and restarts the PHR Periodic Timer. UE 101 repeats thisoperation.

Additionally, UE 101 resets the MAC in order to receive a handovercommand from an ENB of the source cell. In the MAC reset process, UE 101stops all timers in operation, including the PHR Periodic Timer. Becausethe PHR Periodic Timer is then restarted only when the PHR is generated,the stopped PHR Periodic Timer is not restarted unless a new PHR isgenerated in a target cell.

Therefore, if only the periodic PHR is set in the UE, excluding theregular PHR, the new PHR is generated only at the expiration of the PHRPeriodic Timer. However, because the PHR Periodic Timer was stopped andwill not restart, due to the MAC reset as described above, the UE may nolonger generate the periodic PHR after its handover to the target cell.

SUMMARY OF THE INVENTION

The present invention is designed to address at least theabove-described problems and/or disadvantages in the prior art and toprovide at least the advantages as will be described below. Accordingly,an aspect of the present invention is to provide a method and apparatusfor preventing transmission interruption of scheduling informationtransmitted from a UE to an ENB in a wireless communication system.

Another aspect of the present invention is to provide a method andapparatus for preventing transmission interruption of available transmitpower information transmitted from a UE to an ENB in a wirelesscommunication system.

Another aspect of the present invention is to provide a method andapparatus for reporting available transmit power information of a UE,upon an occurrence of a MAC reset in a wireless communication system.

Another aspect of the present invention is to provide a method andapparatus for resuming transmission of available transmit powerinformation of a UE, upon an occurrence of a MAC reset in a wirelesscommunication system.

In accordance with an aspect of the present invention, a method forreporting available transmit power information to a base station by a UEin a wireless communication system is provided. The method includesreceiving, by the UE, an uplink resource, determining whether the uplinkresource is a first uplink resource allocated for a new transmissionafter a Medium Access Control (MAC) reset, starting a timer forreporting the available transmit power information, if the allocateduplink resource is the first uplink resource allocated for the newtransmission after the MAC reset, and reporting the available transmitpower information, upon expiration of the timer.

In accordance with another aspect of the present invention, a UEapparatus for reporting available transmit power information to a basestation in a wireless communication system in provided. The UE apparatusincludes a transceiver for transmitting and receiving messages over awireless channel; a Medium Access Control (MAC) processor for performinga MAC process for communication with the base station; and a controllerfor controlling periodic transmission of the available transmit powerinformation depending on whether a received uplink resource is a firstuplink resource allocated for a new transmission after a MAC reset.

In accordance with another aspect of the present invention, a method forreporting available transmit power information to a base station by a UEin a wireless communication system is provided. In the method, the UEdetermines whether a received uplink resource is a first uplink resourceallocated for a new transmission after a MAC reset, and generates andtransmits the available transmit power information to the ENB, if theallocated uplink resource is the first uplink resource allocated for thenew transmission after the MAC reset.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a diagram illustrating a configuration of an LTE system;

FIG. 2 is a flowchart illustrating an operation of a UE according to anembodiment of the present invention;

FIG. 3 is a flowchart illustrating an operation of a UE according to anembodiment of the present invention;

FIG. 4 is a flowchart illustrating an operation of a UE according to anembodiment of the present invention;

FIG. 5 is a flowchart illustrating an operation of a UE according to anembodiment of the present invention; and

FIG. 6 is a block diagram illustrating a UE apparatus according to anembodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the annexed drawings. In the followingdescription, a detailed description of known functions andconfigurations incorporated herein has been omitted for clarity andconciseness, i.e., to avoid obscuring the invention in unnecessarydetails. Terms used herein are defined based on functions in the presentinvention and may vary according to users, operator intention, or usualpractices. Therefore, the definition of the terms used herein should bebased on contents throughout the specification.

As described above, an aspect of the present invention is to provide amethod and apparatus for solving problems that occur in a conventionalUE, in which only a periodic PHR is set, wherein the UE no longergenerates a PHR in a target cell due to a MAC reset after performing ahandover to the target cell. Accordingly, herein below in thisspecification, the term “PHR” is to be construed as “a periodic PHR”unless stated otherwise.

While certain embodiments of the present invention will be described inconnection with the LTE system illustrated and described in FIG. 1, thesame may be applied to any system in which a mobile stationcorresponding to the UE transmits available transmit power informationor scheduling information needing periodic transmission to a basestation corresponding to the ENB. That is, the present invention may beapplied in the same way to any system in which a UE starts a timer fortransmission of scheduling information and the timer is reset uponhandover of the UE.

In accordance with an embodiment of the present invention, after a MACreset occurs in a UE, the UE stops all timers, except for a timerinvolved in the generation of a PHR.

In accordance with another embodiment of the present invention, after aMAC reset occurs in a UE, the UE stops all timers therein and thenrestarts a timer involved in generation of a PHR, upon completion of theMAC reset.

In accordance with another embodiment of the present invention, after aMAC reset occurs in a UE, the UE restarts a timer involved in thegeneration of a PHR, after receiving a first uplink grant from an ENB.

In accordance with another embodiment of the present invention, after aMAC reset occurs in a UE, the UE generates a PHR after receiving a firstuplink grant from the ENB.

As the above-mention embodiments of the present invention are describedin more detail below, it will be assumed that the MAC reset occurs inthe UE, upon a handover of the UE. However, the embodiments of thepresent invention may be applied even when the MAC reset occurs forother reasons.

FIG. 2 illustrates an operation of a UE according to an embodiment ofthe present invention, wherein upon occurrence of a MAC reset, the UEcontrols a PHR Periodic Timer.

As described above, one of the problems to be solved by the presentinvention arises because upon a MAC reset in a UE, the UE stops a PHRPeriodic Timer for PHR generation. Accordingly, to address this problem,in accordance with an embodiment of the present invention, asillustrated in FIG. 2, the UE stops all timers therein, except for thePHR Periodic Timer.

Referring to FIG. 2, a MAC reset occurs before handover of a UE in step205. The MAC reset is generally performed prior to starting a handover,and the UE resets the MAC, upon receiving a handover command from anENB.

In step 210, the UE determines if a PHR Periodic Timer is operatingduring the MAC reset. If the PHR Periodic Timer is operating, the UEstops all timers in the UE, except for the PHR Periodic Timer, in step215. However, if the PHR Periodic Timer is not operating during the MACreset in step 210, e.g., if the PHR Periodic Timer is not set, the UEstops all timers in the UE in step 220.

FIG. 3 illustrates an operation of UE according to another embodiment ofthe present invention, wherein upon occurrence of a MAC reset, the UEstops a PHR Periodic Timer, and restarts the PHR Periodic Timer, afterthe MAC reset is completed. By restarting the PHR Periodic Timer afterthe MAC reset is completed, the periodic PHR can be continuouslygenerated, even after the MAC reset.

Referring to FIG. 3, a MAC reset starts, prior to a handover of the UE,in step 305. The UE stops all timers operating in the UE in step 310.The UE proceeds with the remaining MAC reset process in step 315. Theremaining MAC reset process includes, for example, terminating ongoingMAC processes and releasing the resources allocated to the MAC layer.

After the MAC reset process is completed in step 315, the UE determineswhether a PHR Periodic Timer for generation of a PHR was set prior tothe MAC reset in step 320. If the PHR Periodic Timer was previously set,the UE restarts the PHR Periodic Timer in step 325, identifying that thePHR Periodic Timer was stopped in the MAC reset process in step 310, andthen proceeds with a next procedure in step 330. The next procedure mayinclude, for example, a random access process in the target cell. If thePHR Periodic Timer was not previously set in step 320, the UE performsthe next procedure in step 330.

FIG. 4 illustrates an operation of a UE according to another embodimentof the present invention, wherein, the UE restarts a PHR Periodic Timerupon receiving a first uplink grant, after a MAC reset process iscompleted. The UE waits for the first uplink grant to be received froman ENB of the target cell, without immediately restarting the PHRPeriodic Timer, after the completion of the MAC reset process, becausethe UE normally sends an important control message, e.g., a handovercomplete message, using the resource allocated in the first uplinkgrant, after the MAC reset. Accordingly, if the UE were to immediatelyrestart the PHR Periodic Timer, after the MAC reset is completed, the UEwould occasionally transmit a PHR instead of the important controlmessage or a part of the important control message because the PHRPeriodic Timer may expire at the same time the UE should send theimportant control message to the ENB of the target cell, after receivingthe first uplink grant. However, if the UE restarts the PHR PeriodicTimer upon receiving the first uplink grant, after occurrence of the MACreset, as illustrated in FIG. 4, it is possible to prevent the PHR frombeing transmitted during the first uplink transmission.

Referring to FIG. 4, the UE receives an uplink grant indicatingallocation of an uplink resource for new transmission in the target cellfrom an ENB of the target cell in step 405. In step 410, the UEdetermines whether the uplink grant is a first uplink grant to bereceived after a previous MAC reset.

The uplink grant that is the first received uplink grant after the MACreset, is the same as an uplink grant that a UE first receives after ahandover to a target cell. Basically, an uplink grant can be classifiedas an uplink grant for a new transmission and an uplink grant for aretransmission, and in the present invention, the uplink grant is to beconstrued as an uplink grant for a new transmission.

When the uplink grant is the first received uplink grant, after a MACreset, in step 410, the UE restarts a PHR Periodic Timer in step 415.Accordingly, the UE is able to transmit the periodic PHR to the ENB ofthe target cell even after the MAC reset.

However, if the uplink grant is not the first received uplink grant,after a MAC reset, in step 410, e.g., if the operation in step 415 hasalready been performed, the UE proceeds with the uplink transmissionprocess in step 420.

FIG. 5 illustrates an operation of a UE according to another embodimentof the present invention, wherein the UE may transmit a periodic PHR ina target cell, even after a handover is performed, i.e., after a MACreset is completed. Specifically, the UE generates the PHR, aftercompleting the MAC reset process, because the PHR Periodic Timer isautomatically restarted when a PHR is generated.

Referring to FIG. 5, the UE receives an uplink grant from a target cellin step 505. In step 510, the UE determines whether the uplink grant isa first uplink grant to be received since performing a previous MACreset. If the uplink grant is the first uplink grant, the UE generates aPHR in step 515 in order to transmit the periodic PHR after the MACreset, and then performs an uplink transmission process in step 520.Accordingly, the UE can transmit the periodic PHR in the target cell,even after the handover. However, if the uplink grant is not the firstuplink grant received after the previous MAC reset, in step 510, e.g.,if the operation of step 515 has already been performed, the UE directlyperforms the uplink transmission process in step 520.

FIG. 6 illustrates a UE apparatus according to an embodiment of thepresent invention.

Referring to FIG. 6, a UE 600 includes a control message processor 605,a Layer 2 (L2) processor 615, a PHR generator 610, a grant processor620, and a transceiver 625.

The control message processor 605 processes various control messagesthat are transmitted and received over the wireless network. Among otherthings, the control message processor 605 resets the L2 processor 615when a control message received form an ENB includes a handover command.

The L2 processor 615 includes a MAC processor. Upon receipt of a resetcommand from the control message processor 605, the L2 processor 615notifies the PHR generator 610 of the reset of a MAC layer due to theMAC reset.

The PHR generator 610 controls a PHR Periodic Timer for generation of aperiodic PHR. For example, the PHR generator 610 controls the PHRPeriodic Timer to start, restart, and stop.

Upon receiving a MAC reset notice from the control message processor605, the PHR generator 610 may stop or restart the PHR Periodic Timer.More specifically, according to an embodiment of the present invention,as illustrated in FIG. 2, upon occurrence of a MAC reset, the PHRgenerator 610 maintains the running of the PHR periodic timer, eventhough all other timers are stopped in the UE.

According to an embodiment of the present invention, as illustrated inFIG. 3, the PHR generator 610 restarts the PHR Periodic Timer aftercompletion of the MAC reset. According an embodiment of the presentinvention, as illustrated in FIG. 4, the PHR generator 610 restarts thePHR Periodic Timer upon receiving a first uplink grant after completionof the MAC reset. According an embodiment of the present invention, asillustrated in FIG. 5, the PHR generator 610 generates a periodic PHRupon receiving the first uplink grant, after completion of the MACreset. The PHR generator 610 then provides the generated periodic PHR tothe L2 processor 615.

The PHR Periodic Timer (not shown) may be included in the PHR generator610, or may be provided as a separate timer.

The L2 processor 615, which is a Radio Link Control (RLC) device or aMAC device, can frame upper layer data including a Layer 3 (L3) controlmessage in an appropriate size, employ Hybrid Automatic Repeat reQuest(HARQ) operation, and provide a multiplexing function. In addition, theL2 processor 615 restores data provided from the transceiver 625 to itsoriginal upper layer data, and provides it to an appropriate upperlayer. Also, the L2 processor 615 multiplexes a specific control messagelike the PHR and provides it to the transceiver 625.

The grant processor 620 recognizes allocated transmission resources byanalyzing a grant received over a wireless channel. The grant processor620 notifies the PHR generator 610 of a possibility of uplinktransmission, and controls the transceiver 625 so that the transceiver625 may transmit and receive data over the wireless channel using theallocated transmission resources.

The transceiver 625 transmits MAC PDUs provided from the L2 processor615 over the wireless channel. Also, the transceiver 625 receivesdownlink and uplink grants for allocating downlink and uplinktransmission resources from the ENB over the wireless channel, andprovides the grants to the grant processor 620. The transceiver 625processes signals received over the wireless channel and provide them toan appropriate upper layer.

While it is shown in FIG. 6 that the control message processor 605, theL2 processor 615, the PHR generator 610 and the grant processor 620 areseparate devices, some or all of the components may be implemented as asingle controller.

As is apparent from the foregoing description, a UE in accordance withthe present invention is capable of preventing a transmissioninterruption of periodic available transmit power information upon anoccurrence of a MAC reset. Similarly, the UE may also prevent aninterruption of a periodic available transmit power report after ahandover to a new cell.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of a terminal in a wirelesscommunication system, the method comprising: identifying that a mediumaccess control (MAC) reset occurs; if the MAC reset is performed,stopping a periodic power headroom report (PHR) timer; receiving, from abase station, information related to an uplink resource; identifyingwhether the uplink resource is first allocated for a new transmissionsince the MAC reset is performed; when the uplink resource is firstallocated for the new transmission since the MAC reset is performed,starting the stopped periodic PHR timer, even without transmitting aPHR; triggering a PHR, if the started periodic PHR timer expires;transmitting, to the base station, the triggered PHR ; and starting theexpired periodic PHR timer after triggering the PHR.
 2. The method ofclaim 1, wherein the PHR is first transmitted since the MAC reset isperformed.
 3. The method of claim 1, wherein the MAC reset is performedbefore a handover of the terminal.
 4. A terminal in a wirelesscommunication system, the terminal comprising: a transceiver; and acontroller configured to: identify that a medium access control (MAC)reset occurs, if the MAC reset is performed, stop aperiodic powerheadroom report (PHR) timer, control the transceiver to receive, from abase station, information related to an uplink resource, identifywhether the uplink resource is first allocated for a new transmissionsince the MAC reset is performed, start the stopped periodic PHR timer,even without transmitting a PHR, when the uplink resource is firstallocated for the new transmission since the MAC reset is performed,trigger a PHR, if the started periodic PHR timer expires, control thetransceiver to transmit, to the base station, the triggered PHR , andstart the expired periodic PHR timer after triggering the PHR.
 5. Theterminal of claim 4, wherein the PHR is first transmitted since the MACreset is performed.
 6. The terminal of claim 4, wherein the MAC reset isperformed before a handover of the terminal.
 7. A method of a basestation in a wireless communication system, the method comprising:transmitting, to a terminal, first information related to an uplinkresource first allocated for a new transmission since a medium accesscontrol (MAC) reset is performed in the terminal; receiving, from theterminal, a first message to confirm a handover without a power headroomreport (PHR) based on the uplink resource; transmitting, to theterminal, second information related to another uplink resource aftertransmitting the first information; and receiving, from the terminal, asecond message including a PHR based on the another uplink resource. 8.The method of claim 7, wherein the PHR in the second message is firstlytriggered since the MAC reset is performed.
 9. A base station in awireless communication system, the base station comprising: atransceiver; and a processor configured to control the transceiver to:transmit, to a terminal, first information related to an uplink resourcefirst allocated for a new transmission since a medium access control(MAC) reset occurs is performed in the terminal; receive, from theterminal, a first message to confirm a handover without a power headroomreport (PHR) based on the uplink resource; transmit, to the terminal,second information related to another uplink resource after transmittingthe first information; and receive, from the terminal, a second messageincluding a PHR based on the another uplink resource.
 10. The basestation of claim 9, wherein the PHR in the second message is firstlytriggered since the MAC reset is performed.